Some hard-to-reach places are served by tower-crane mounted conveyors.

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Teake Zuidema

Some hard-to-reach places are served by tower-crane mounted conveyors.

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Concrete on the Move at the Canal

Much of the concrete used at the Panama Canal would be very difficult to pump, due to low slumps, large aggregate, and difficult gradations. This led Grupo Unidos por el Canal (GUPC) to buy 36 Maxon Agitor trucks to move the concrete from the production plant to the project. These truck bodies do not turn but have an auger to keep the concrete agitated during the 15 minutes it takes to go from filling at the batch plant to discharge.

To regulate the feed of concrete to the Telebelts, GUPC is using Maxon Surgecrete hoppers. “The belts can only take a certain delivery rate,” says Bill Maxon, president of Milwaukee-based Maxon Industries, a supplier of concrete equipment. “The Surgecrete allows the trucks to dump their loads quickly and return to the batch plant. This maximizes productivity and minimizes waiting time and allows a continuous flow of concrete on the belts.”

With the high ambient temperatures, and in response to the requirement to keep the concrete cool, all of the Agitor agitator trucks are insulated with 3 inches of closed cell foam and roll-back tarps to maintain the 52 degree F temperature of the concrete. “The insulation also kept the truck’s shell cool,” says Maxon. “And the tarp covers kept the concrete dry during the frequent rainy periods.”

—­William D. Palmer Jr., editor in chief, Concrete Construction

The world’s largest ongoing construction project is the expansion of the Panama Canal, adding a third lane to allow larger ships to traverse the isthmus. The joint venture that is building the new locks and dams has demanded an extra $573 million for the job. Making the right concrete mix was its greatest challenge.

In 2009, Grupo Unidos por el Canal (GUPC) won the contract to build larger locks on both entrances of the Panama Canal with a low bid of $3.1 billion. The joint venture is formed by Spanish contractor Sacyr Vallehermoso, Italian Impregilo, Belgian Jan de Nul, and Panama’s Constructora Urbana. Most of the excavation (a total of 45.5 million cubic yards) is now complete, and the project is mainly about placing rebar and casting concrete. However, GUPC is six months behind schedule due to problems with producing the right mix for the marine concrete.

The requirements from the Panama Canal Authority (ACP) are high since the operator of the canal wants a design-life of 100 years in an area that is seismically active. This means, among other things, that saltwater cannot reach the rebar embedded in the marine concrete during that period. “It took GUPC six months before they came up with a concrete that passed the ASTM C1202 test for marine concrete,” says Abdiel Julio, of ACP’s public relations department. GUPC claims ACP misstated the quality of the basalt aggregate and was slow in approving the mix. It is demanding the $573 million to compensate for unforeseen costs.

“The problem was that the crushed basalt out of the excavation that we used as aggregate contained much more fines than we were led to believe,” says Jan Kop, the Dutch project manager for Jan de Nul. The giant crusher GUPC built on the Pacific side of the canal has to remove 30 percent of the fines from the basalt. “Our concrete mix passed the test after we removed more fines and added more cement and silica fume to make it more impermeable,” says Kop.

Concrete production

The two concrete plants on both construction sites are humming along now, and together, produce 160,000 tons of concrete per month. In all, the project will need 6.5 million cubic yards of concrete and 250,000 tons of reinforcing steel. Both sets of locks consist of three lock chambers that each are 140 feet long, 180 feet wide, and 59 feet deep. Although they are larger than the existing locks, they will use less water. A gravity-based system of saving basins, water tunnels, and culverts makes it possible to recycle 60 percent of the water from each passing ship.

Both concrete plants are designed to produce 21 yards in five minutes. With ambient temperatures reaching 37 degrees C (100 degrees F), temperature control is essential and all concrete production, transport, and casting is embedded with cooling systems. According to specifications, the temperature of the mix must be within 7.7 degrees C (14 degrees F) at all times. Forced cooling systems on both sides are capable of making 670 tons of ice each day. Huge tents prevent the sun from warming the sand and the coarse aggregate.

The heavy traffic and the vastness of the almost one-mile-long site complicates the transfer of the concrete. A fleet of open-bed, nine-yard trucks, conveyor belts, and concrete pumps transports the concrete. Most concrete is delivered to its final destination by a Putzmeister TB130 telescopic belt conveyor or its bigger cousin, the TB200. Some hard-to-reach places are served by tower-crane mounted conveyors. More than 21 million square feet of concrete must be formed.

Panama gets a lot of rain, which is good for the canal but a problem for casting concrete. “We cast the concrete in layers with one low point,” says Kop. “When it rains, all of the water runs to the lowest point from where we can easily remove it. When it rains for a long period, we stop pouring, and then we have to deal with an unforeseen cold joint that demands extra attention before we can move on.”

The ACP had planned to open the expanded canal in October 2014, 100 years after completion of the original canal. The opening is now expected to be in spring 2015. GUPC faces penalties of $300,000 for every day the project is delivered after Oct. 21, 2014. Once the new locks are open, Post-Panamax ships, much larger than those that currently navigate the canal and carrying 12,600 containers, will traverse the famous waterway. TCP

Teake Zuidema is a Dutch freelance photographer/journalist living in Pittsburgh.